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A viral infection does not always cause disease. A viral infection simply involves viral replication in the host, but disease is the damage caused by viral multiplication. [5] An individual who has a viral infection but does not display disease symptoms is known as a carrier. [17] Mechanisms by which viruses cause damage and disease to host cells
Many viruses can exist inside a host for long periods during which little damage is done. Extremely virulent strains can eventually evolve by mutation and natural selection within the virus population inside a host. The term "neurovirulent" is used for viruses such as rabies and herpes simplex which can invade the nervous system and cause ...
When the virus replicates faster than the immune system can control, it can destroy cells and harm the body, and it can even incite an over-zealous immune reaction that can cause other damage. Not ...
Viruses also have notable virulence factors. Experimental research, for example, often focuses on creating environments that isolate and identify the role of "niche-specific virulence genes". These are genes that perform specific tasks within specific tissues/places at specific times; the sum total of niche-specific genes is the virus' virulence.
Viruses can, and do, turn our world upside down. But they also made us into what we are today.
Some viruses, such as Epstein–Barr virus, often cause cells to proliferate without causing malignancy; [46] but some other viruses, such as papillomavirus, are an established cause of cancer. [47] When a cell's DNA is damaged by a virus such that the cell cannot repair itself, this often triggers apoptosis.
Most viruses that enter can be opportunistic and accidental pathogens, but some like herpes viruses and rabies virus have evolved in time to enter the nervous system efficiently, by exploiting the neuronal cell biology. While acute viral diseases come on quickly, chronic viral conditions have long incubation periods inside the body.
The virus may induce the cell to forcefully undergo cell division, which may lead to transformation of the cell and, ultimately, cancer. An example of a family within this classification is the Adenoviridae. There is only one well-studied example in which a class 1 family of viruses does not replicate within the nucleus.